1. Field of the Invention
The present invention relates to a method for manufacturing a hard, water-resistant anti-fog coating, and particularly relates to a method for manufacturing a hard, water-resistant anti-fog coating on plastic material.
2. Description of the Prior Art
The fundamental of anti-fog property is to form a hydrophilic surface on a base material wherein water drops condensed by the hydrophilic surface have little contact angle on the surface of the base material to naturally form a continuous or substantial continuous water film for avoiding light scattering resulted from the water drops and for maintaining the original optical transmittance of the base material.
Preparing methods for a hydrophilic surface are classified into three: (1) a hydrophilic agent is directly introduced into a polymer processing process to form a hydrophilic surface on the surface of the base material. Although this method has a simple process and it is easy to operated, but the hydrophilic agent will diffuse to the surface of the base material and diffuse from the surface into the air. Therefore, the hydrophilic agent will disappear with time. as a result, the surface of the base material can not maintain it's hydrophilic property for a long time and the hydrophilic surface disappears with time. Therefore, this method only can be used to be packages of foods having shorter life cycles. (2) The surface of the base material is chemically modified directly to form a hydrophilic film on the surface of the base. Therefore, the hydrophilic groups are difficult to depart from the surface of the base material, and the surface of the base material can get good hydrophilic property. However, this method has critical limit for size of base material and processing conditions, and the hardness of the hydrophilic surface formed by this method is bad. (3) Hydrophilic groups are introduced into a coating, and then, a hydrophilic film is formed on the base material by coating technology, photo curing technology, or heat curing technology. Although foregoing three methods can be utilized to treat surfaces of various base materials and the hydrophilic (coating) film (anti-fog coating (film)) manufacturing by these methods is a single-layered structure, but in these methods, it is easy for water to intrude between the hydrophilic film and the base material because of the hydrophilic groups. And it results in loss and disappearance of the hydrophilic (coating) film (anti-fog coating (film)) adhesion of the hydrophilic (coating) film (anti-fog coating (film)). Currently, for preparing a hydrophilic (coating) film (anti-fog coating (film)), an inorganic oxide, for example TiO2, ZnO, or ZrO2, is used to prepare a coating, and then, the coating is coated on a glass material or a ceramic material and it is treated with high temperature to get good adhesion. Although the coating (film) has good hydrophilic property and high hardness, but the high temperature treatment brings a limit that only some kinds of base materials can be utilized by this method. Therefore, some base materials which can not sustain high temperature can be utilized, and particularly, the plastic material can be utilized.
Currently, expect the anti-fog property of the hydrophilic (coating) film, people have more and more respect for the easy-to-clean property of the hydrophilic (coating) film. Generally, hydrophilic groups have both of hydrophilic property and lipophilic property because the hydrophilic groups have high surface energy. Except mist, there are many organic compounds existing in nature environment. The anti-fog ability of the hydrophilic (coating) film is decreased because the organic compounds existing in nature environment are adhered to the hydrophilic (coating) film or fingerprints are attached to the hydrophilic (coating) film. Therefore, it often has a need of washing the hydrophilic (coating) film with water. However, it is easy for the hydrophilic (coating) films, which are manufactured by foregoing three methods, to be intruded by water and it results in disappearance of the adhesion of the hydrophilic (coating) films because of existing of the hydrophilic groups. The adhesion of the hydrophilic (coating) films is decreased through frequently washing. Therefore, the lifetime of the hydrophilic (coating) films is substantially decreased.
Besides, there are some problems for manufacturing an anti-fog coating (film) on a plastic material: First, the plastic material is sensitive to temperature (or heat) and solvent, and it is difficult to chemically modify the plastic material. If the anti-fog coating (film) is manufactured by coating the hydrophilic coating on the plastic material, it is easy for water to intrude between the anti-fog coating (film) and the plastic material because of existing of the hydrophilic groups and it results in disappearance of adhesion of the anti-fog coating (film). Therefore, it has a need to improve the adhesion between the anti-fog coating (film) and the plastic material in high humidity environment for avoiding the anti-fog coating (film) peeling off form the plastic material. Final, the anti-fog coating (film) manufactured by the conventional method, in which the hydrophilic coating is coated on the plastic material, is not hard enough to avoid scraping and damaging. Therefore, it is not practical.
Therefore, it has a need of a method for manufacturing a hard, water-resistant anti-fog coating on plastic material by which the drawbacks of the conventional methods can be overcome and the adhesion, hardness, and water resistance of the anti-fog coating can be improved. Therefore, an anti-fog coating which is adhered to the plastic material well and has high hardness and high water resistance, is prepared by this method. Furthermore, an anti-fog coating, which is difficult to be intruded and broken by water and can be washed frequently, can be provided by this method, too.